Early cancellation of my wifi contract

You don't have a WiFi contract (there is no such thing - WiFi is the router's wireless connection within your home).

You have a broadband contract with o2 with a minimum term of 24 months? There is no possibility to terminate this early unless you are leaving the country permanently or moving to an address where o2 is unable to provide the service in the contract. Do either if these cases apply?

i have moved out of germany permanently at the end of august. 

Then you can submit your termination request here: https://info.o2online.de/kuendigung/

Make sure you select außerordentliche Kündigung and enter moving abroad as the reason. You will need to upload the document confirming your deregistration  in Germany and a document proving you are living in a different country. You will then only have to pay for one more month.

here on this post?

Hello ​@danial.akid,
thank you for posting your question here in the community. If you would like to terminate your contract early due to a permanent move abroad, we have compiled all the relevant information in this article. How to do a cancellation of my DSL contract due to moving abroad? Please take a look and get in touch with us again if you have any further questions.
Kind regards, Bianca
 

here on this post?

No! Follow the link to the online form.

Good morning ​@danial.akid.

If you have any further questions about termination or other topics, please feel free to contact us here at any time 😊